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ŠUMARSKI LIST 5-6/2012 str. 41     <-- 41 -->        PDF

population differentiation as the difference between FST and FST corrected for null alleles was by one order of magnitude lower than both of the calculated indices (data not shown). Differentiation between populations measured as FST (FST = 0.018, P = 0.000), was so far the lowest in Europe. It was lower than the one obtained for populations of common ash in Bosnia (0.023; Ballian et al. 2008), Britain (0.025; Sutherland et al. 2010), western and central Europe (0.027; Heuertz et al. 2004), Italy (0.049; Ferrazzini et al. 2007), Bulgaria (0.087; Heuertz et al. 2001) and at the European level (0.076; Heuertz et al. 2004). Though statistically significant, the differentiation between populations measured as FST might not be biologically significant, because variation of adaptive loci is not necessarily correlated to highly variable loci such as microsatellites used here (Hedrick 1999). Even after omitting population Rodik of non-autochthonous origin from the dataset, the FST value remained the same, showing that population Rodik comes from the same gene pool as the other analysed populations. Construction of neighbor-joining and UPGMA trees also failed to detect structure among populations as well as no positive relationship between geographical and genetic distances was observed. Lack of differentiation between populations is most likely explained by the fact that common ash is a wind pollinated tree species, where pollen and seed can travel over substantial distances (Bacles et al. 2005, Bacles et al. 2006, Bacles and Ennos 2008), the largest between any of the studied population pairs being 92 km.
The level of inbreeding is an important indicator for the quality of a seed stand since heterozygotes are thought to be more resilient to environmental stress (Namkoong 1998, Farris and Mitton 1984). Therefore homozygosity should be taken into consideration when selecting seed stands to ensure seed quality, long-term survival of seedlings/trees and their adaptability. In the case of seed stand Rodik, which is of non-autochthonous origin, the positive inbreeding coefficient (FIS = 0.182, P = 0.000), indicating excess of homozygotes, was high and statistically significantly different from zero and remained so also after the exclusion of locus FEMSATL16 (FIS = 0.106, P = 0.001). In the same stand, number of alleles and observed heterozygosity were lower than the average over all five stands, while gene diversity and number of effective alleles were little above the average. The results, especially high inbreeding coefficient, could be explained with the artificial establishment of the stand with reproductive material that had possibly a narrower genetic base in comparison to natural regeneration. The observed inbreeding coefficient in this population was nevertheless lower than the one found in common ash populations from France (Morand et al. 2002) and Italy (Ferrazzini et al. 2007). According to Miyamoto et al. (2008), results based on the sample size of 30 individual ash trees are biased for estimation of the number of alleles and num­b­er of effective alleles, but in our case the first index was under and the latter above the Slovenian average. For collection of forest reproductive material from seed stand Rodik good seed collection practice is therefore advised to evade establishment of new forests with restricted genetic diversity and poor adaptive potential. Collection of approximately equal amounts of seed from as many as possible, within the stand equally spaced trees, is essential to maximise genetic diversity of the reproductive material. Number of alleles, effective alleles, observed and expected heterozygosity in seed stand Grofija were higher than the Slovenian